SN3
SHORT NOTE
5M
★ High-yield
Describe the basal ganglia with their connections and functions. Add a note on their disorders.
Definition
The basal ganglia are subcortical masses of grey matter concerned with the planning and control of movement.
| Grouping | Components |
|---|---|
| Corpus striatum | Caudate nucleus + lentiform nucleus |
| Lentiform nucleus | Putamen (lateral) + globus pallidus (medial) |
| Neostriatum (striatum) | Caudate + putamen — the input nuclei |
| Palaeostriatum | Globus pallidus — the output nucleus |
| Functionally associated | Substantia nigra (midbrain) and subthalamic nucleus |
- The caudate and putamen are separated by the internal capsule but joined by bridges of grey matter, giving the striated appearance that names the striatum
Connections
| Pathway | Net effect | Dopamine acts on it |
|---|---|---|
| Direct | Facilitates movement | Excites (D1 receptors) |
| Indirect | Inhibits movement | Inhibits (D2 receptors) |
- Dopamine from the substantia nigra therefore promotes movement by both routes — exciting the facilitatory pathway and inhibiting the inhibitory one
- The nigrostriatal pathway uses dopamine; the striatal interneurones use acetylcholine; the output is GABAergic
Functions
- Initiation and regulation of voluntary movement
- Control of muscle tone
- Suppression of unwanted movement
- Automatic and learned motor sequences — walking, writing, the arm swing
- Roles in cognition, motivation and emotion through parallel loops
Disorders
| Disorder | Lesion | Features |
|---|---|---|
| Parkinson disease | Degeneration of the substantia nigra — loss of dopamine | Resting "pill-rolling" tremor, rigidity (cogwheel), bradykinesia, postural instability; mask-like face, festinant gait |
| Huntington disease | Degeneration of the caudate and putamen | Chorea, dementia, psychiatric change; autosomal dominant, CAG repeat expansion |
| Hemiballismus | Subthalamic nucleus (usually a small stroke) | Violent flinging movements of the contralateral limbs |
| Athetosis | Striatum | Slow writhing movements of the distal limbs |
| WILSON disease | Copper deposition in the lentiform nucleus | Tremor, dystonia, dysarthria; Kayser–Fleischer rings |
Applied Aspects
- Levodopa with carbidopa replaces dopamine in Parkinson disease; carbidopa blocks peripheral decarboxylation, so more reaches the brain
- Symptoms appear only when about 70–80% of nigral neurones are lost, which is why the disease presents late and why neuroprotection has proved so difficult
- Deep brain stimulation of the subthalamic nucleus or globus pallidus is effective in advanced disease — a direct application of the circuit anatomy
- Drug-induced parkinsonism from antipsychotics blocking D2 receptors is common and reversible; it must not be mistaken for the idiopathic disease
- Wilson disease must be excluded in any young person with a movement disorder — it is one of the few treatable causes
All questions in Neuroanatomy
- Q1Describe the external features and internal structure of the spinal cord. Describe its ascending and descending tracts and add a note on its lesions. ★
- Q2Describe the functional areas of the cerebral cortex and the blood supply of the cerebrum. Add a note on aphasia. ★
- Q3Describe the cerebellum under divisions, peduncles, connections and functions. Add a note on the signs of cerebellar disease. ★
- Q4Describe the parts of the brainstem and the arrangement of the cranial nerve nuclei. Add a note on the brainstem syndromes. ★
- Q5Describe the meninges and the ventricular system. Explain the formation, circulation and absorption of cerebrospinal fluid and add a note on hydrocephalus. ★
- SN1Describe the internal capsule with its parts, contents and blood supply. Add a note on capsular stroke. ★
- SN2Describe the circle of Willis with its formation and significance. Add a note on berry aneurysm. ★
- SN3Describe the basal ganglia with their connections and functions. Add a note on their disorders. ★
- SN4Describe the thalamus with its nuclei and connections. Add a note on the thalamic syndrome. ★
- SN5Describe the visual pathway and the effects of lesions at different levels. Add a note on the light reflex. ★
- SN6Describe the hypothalamus with its nuclei, connections and functions. ★
- SN7Compare the sympathetic and parasympathetic nervous systems. Add a note on Horner syndrome.